The present invention relates to bulk starter media for cheesemaking and, in particular, to a bulk starter media which contains particulate, insoluble materials as neutralizing agents. In the commercial production of cheese, large vats of milk are treated with a milk clotting agent such as rennin and inoculated with lactic acid producing bacteria such as Streptococcus lactis, S. cremoris, S. thermophilus and Lactobacillus bulgaricus. These lactic acid producing bacteria are capable of fermenting lactose or other similar carbohydrates to produce lactic acid.
The bacteria is generally propagated from a mother culture in large enough quantities of aqueous medium to produce a bulk starter which can then be used for fermenting the final batch of milk to produce cheese as the final product. In a typical procedure, a bulk starter medium is prepared by dissolving a dry powder comprising a nutrient base and a growth stimulant, together with alkali metal phosphate and/or polyphosphate phage control agents in water to a level of about 8% solids. The solution is sterilized and cooled whereupon it is inoculated with the lactic acid producing bacteria which is allowed to incubate. After incubation, the "ripened" starter is added to the cheese milk at a level of from about 1/2 to 3/4 volume percent. The cheese milk at this point will have a pH of approximately 6.6, however, as the bacteria grows, the acid it produces will gradually lower the pH.
Neutralization is very important to the growth of the lactic acid producing bacteria because the acid produced impairs the growth of the bacteria and will eventually kill them, especially at a pH of 4.8 or below. Neutralization can be accomplished by the continuous addition of a water soluble base or an aqueous basic solution such as sodium hydroxide or ammonia gas so as to provide a pH which is maintained at 5.2 or above. Specialized equipment has been developed to monitor the pH of the growth medium and to add the neutralizing agent as needed. More recently, there has been disclosed in U.S. Pat. No. 4,282,255 the use of an essentially water insoluble or temporarily water insolubilized and thus initially solid form of a neutralizing agent. This patent mentions the use of magnesium phosphate and magnesium ammonium phosphate in particular. A magnesium ammonium phosphate neutralizing system in which magnesium ions, ammonium ions and phosphate ions are provided so as to form insoluble magnesium ammonium phosphate in situ is disclosed in U.S. Pat. No. 4,402,986.
While the employment of essentially insoluble or temporarily insolubilized neutralizing agents eliminates the need for the constant addition of base, their use presents another problem because of their insolubility. This is the case because the presence of the insoluble neutralizing agent requires agitation to keep it in suspension. This agitation adds cost to the process and is traditionally considered an undesirable procedure because culture growth may be detrimentally affected due to oxygen incorporation into the ripening starter. Accordingly, it would be desirable and it is an object of the present invention to provide a method for maintaining a particulate, insoluble material as neutralizing agent suspended in the ripening starter without the need for agitation.